The US Army has identified a need to achieve broad spectrum chemical protection for breathing equipment supplied for individual and collective protection applications. This need has arisen due to threats associated with toxic industrial chemicals (TICs). Toxic industrial chemicals are defined as chemicals that are manufactured on an industrial scale and readily used and transported around the globe. Examples of TICs for which chemical protection is desired include, but are not limited to, ammonia (NH3), sulfur dioxide (SO2), chlorine (Cl2), hydrogen cyanide (HCN), nitrogen dioxide (NO2) and hydrogen sulfide (H2S). There is also a need to provide safe breathing for first responders and military personnel, among others, who enter chemically contaminated areas to lend assistance and contain the toxic chemical spill. For these situations/scenarios, the chemical threat is often unknown at the time of the toxic chemical release. As a result, it is often not feasible to analyze the air stream for the toxic gas, then select a respirator specifically designed to remove the toxic gas. It is also not feasible, from a cost and logistic aspect, to retain or transport a number of dissimilar respirators to handle the range of the threat. Therefore, the desire is for one respirator to meet the demands of the broad spectrum toxic chemical challenge.
There is also a need to provide safe breathing for personnel working in hazardous environments in the event of a chemical spill, for example, or for those working with or operating processes that utilize or generate toxic vapors. In yet further applications, many hazardous chemicals are employed on an industrial scale, and there is a need to scrub the process streams of these chemicals prior to venting the stream to atmosphere. One additional application involves power plants, where both SO2 and NH3 are eluted from the process. As SO2 oxidizes to SO3, it will react with the NH3 and water forming ammonium bisulfate (NH4)HSO4 and/or ammonium sulfate ((NH4)2SO4), which will crystallize and plug downstream unit operations. A filtration media capable of simultaneously removing large amounts of both NH3 and SO2 would alleviate said burdens.
In order to remove both NH3 and acid gases, a filtration material must possess both acid and basic sites. Amines, such as for example NH3 and methylamine (CH3NH2) are readily removed by reactions involving mineral acids, such as for example HCl and H2SO4, according to reactions:NH3+HCl→NH4Cl2NH3+H2SO4→(NH4)2SO4 2CH3NH2+H2SO4→(CH3NH2)2SO4 Which yield solids and are well known to one skilled in the art. Ammonia will also undergo similar reactions with metal salts, such as for example:2NH3+ZnCl2+H2O→2NH4Cl+ZnO2NH3+NiSO4+H2O→(NH4)2SO4+NiO
On the other hand, basic sites are required for the removal of acid gases. For example:Zn(OH)2+2HCl→ZnCl2+2H2OCuO+SO2→CuSO3 ZnO or Zn(OH)2+2HCN→Zn(CN)2+(1 or 2)H2OThe above reactions are stoichiometric in nature.
For a single filtration material to facilitate reactions involving the removal of amines, such as NH3, and acid gases, such as SO2, the material must possess a high concentration of both acid and basic sites. Otherwise, sufficient filtration capacity for each class of toxic chemicals will be insufficient. Materials with acidic and basic properties have been reported and are known to one skilled in the art. These include zeolites, aluminas, silicas and silica-aluminas, for example. These materials, however, have a relatively low number of either acidic sites or basic sites, and are thus not able to sufficiently facilitate filtration of both acidic and basic materials.
It is also difficult to impregnate materials with components that are both acidic and basic. This is because the two dissimilar functionalities will tend to neutralize each other. Doughty et al. (U.S. Pat. No. 5,492,882) reports the co-impregnation of activated carbon using solutions of copper carbonate, zinc carbonate, and ammonium dimolybdate dissolved in an ammonium carbonate/ammonium hydroxide solution. The authors add copper sulfate, zinc sulfate or ammonium sulfate as the ammonia removal function. The material also contains pre-adsorbed water, which is known to one skilled in the art to enhance removal of ammonia, as NH3 is soluble in water. Doughty et al. report that the material is able to remove both NH3 and SO2 to levels sufficient to meet/exceed CEN Requirements. Although not reported in the patent, subsequent testing/evaluation of the material demonstrates that the filtration capability decrease significantly over time, such as following storage and/or exposure to humid air. These results indicate that the material is not stable.
As such, there is a need for a stable material that is capable of removing or sequestering both acid and basic gases. The inclusion of such materials in filtration apparatuses or safety systems such as breathing apparatuses is greatly desired.